/*  cd4021Vv3
 11/03/2024

 This version will work with as many CD4021's as needed.
 All data is stored in the myButtons[] array

 Many thanks to runaway_pancake for writing some code
that got me pointed in the right direction

//        Demo4021
//         
//        A   --1    16--   +
//        x   --2    15--   B
  dataPin/SO  --3    14--   C
//        E   --4    13--   D
//        F   --5    12--   x
//        G   --6    11--   +
//        H   --7    10--   clk
//      gnd   --8     9--   latch
*/

#define NUMCD4021CHIPS 2
byte myButtons[NUMCD4021CHIPS];//sets the array to the number of chips

int latchPin = 8;
int clockPin = 7;
int dataPin = 9;

unsigned long currentMillis;
unsigned long delayMillis;
int delayTimer = 2000;//2 seconds




void setup (){
  Serial.begin(9600);
  Serial.println("cd4021Vv3");
  pinMode (latchPin, OUTPUT);
  pinMode (clockPin, OUTPUT);
  pinMode (dataPin, INPUT);
 
}

void loop (){
  int q;
  int w;
  currentMillis = millis();
  if(currentMillis - delayMillis >= delayTimer){
    delayMillis = currentMillis;
    
    //This sets the system up to read the data
    latch4021(latchPin);//This function MUST be called before the get4021Byte() is called
    for(q=0;q < NUMCD4021CHIPS;q++){
      myButtons[q] = get4021Byte(dataPin,clockPin); //Put the bytes into the myButtons[] array  
    }
    //At this point all the data is in the myButtons[] array and can be used as required
    

    //This just shows the results
    
    for(w=0;w < NUMCD4021CHIPS;w++){
      Serial.print("myButtons[w] : ");
      Serial.print(w);
      Serial.print(" = ");
      Serial.println(myButtons[w],BIN);
      for(q=0;q<8;q++){//work though the bytes
        if(bitRead(myButtons[w],q) == 1){//if a bit is set
          Serial.print("Button Pressed : ");//tells us the button pressed 0-7
          Serial.println(q);
        }
      }
      Serial.println(" ");
    }
  }
}

void latch4021(int funcPin){
  digitalWrite (funcPin, HIGH);
  delayMicroseconds(5); //works... I want the smallest stable value possible
  digitalWrite (funcPin, LOW);
}

byte get4021Byte(int funcDataPin, int funcClockPin){
  byte registerContent;
  int bitContent;
  for (int idx = 0; idx < 8; idx++)
  {
    bitContent = digitalRead (funcDataPin);
    if (bitContent == 1)
    {
      bitWrite (registerContent,idx,1);
    }
    else
    {
      bitWrite (registerContent,idx,0);
    }
    digitalWrite (funcClockPin, LOW);
    delayMicroseconds(5); //works... I want the smallest stable value possible
    digitalWrite (funcClockPin, HIGH);
  }
  return registerContent;
}